Middle-IR (2–20μm) nonlinear optical (NLO) material has greatly important applications, such as, optoelectronic devices, resource exploration and communications. The prerequisite of an NLO material is crystallographically noncentrosymmetric (NCS) with strong polarity. The design and development of novel middle-IR NLO materials are of great challenge.

The research group headed by Prof. CHEN Ling at Fujian Institute of Research on the Structure of Matter (FJIRSM), Chinese Academy of Sciences (CAS), has proposed new pre-design strategies that include organization of the NLO functional group, modification by ionic group, and the control of the asymmetry. Guided by these strategies, a series of novel NLO materials with very strong SHG response in middle-IR have been discovered.

The distorted GaS₄ tetrahedron is one of the important structure building units in mid-IR NLO materials. Such a building unit constructs the commercial IR NLO material AgGaS₂. Although Ba/Ga/S system may exist some promising candidates for IR NLO materials, only two examples (BaGa₄S₇ and BaGa₂GeS₆) in Ba/Ga/S are noncentrosymmetric, most of them are centrosymmetric compounds. These suggest that the rigid 3D anionic networks in these two examples can generate the NCS structures, meanwhile, the strong localized covalent bond interactions within such networks reduce the polarization, as a result, the SHG intensities of these known examples are weak.

Prof. CHEN Ling’s research group creatively proposed a new synthesis thought, that is to involve a second building unit, SbS₃ pyramid, to help generate an asymmetric structure, Ba₂₃Ga₈Sb₂S₃₈ (BGSbS), which exhibits a strong SHG intensity about 22 times that of AgGaS₂ at 2.05μm radiation laser with the particle size of 46–74μm. This research provides a new route towards the synthesis of new IR NLO materials. (J. Am. Chem. Soc., 2012, 134, 6058–6060).

　　　　　　　  Figure 1. Structure of orthorhombic BGSbS (Ba₂₃Ga₈Sb₂S₃₈) with unit cell marked.

The research group has also discovered several other crystals which may be good potential NLO materials, such as La₄InSbS₉（J. Am. Chem. Soc., 2012, 134, 1993–1995）; Ba₃AGa₅Se₁₀Cl₂ (A = Cs, Rb, K) （J. Am. Chem. Soc., 2012, 134, 2227–2235）; Ln₄GaSbS₉（J. Am. Chem. Soc., 2011, 133, 4617–4624）; Pb₂B₅O₉I（J. Am. Chem. Soc., 2010,132, 12788–12789）; La₂Ga₂GeS₈ and Eu₂Ga₂GeS₇（Inorg. Chem., 2011, 50, 12402–12404）.

Contact:

Prof. CHEN Ling

Fujian Institute of Research on the Structure of Matter

Chinese Academy of Sciences

Email: chenl@fjirsm.ac.cn